Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751256AbdLZS36 (ORCPT ); Tue, 26 Dec 2017 13:29:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:57080 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750890AbdLZS34 (ORCPT ); Tue, 26 Dec 2017 13:29:56 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 72FFF2190E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=robh@kernel.org X-Google-Smtp-Source: ACJfBosiNWr3i6zwuFPN2LVSF1rKvsv8hzIVc8cMdxSkT8tCO4Uz0s4GBSf24RVazlBwZQ+gJ9VCRIHYu30BvWJnCkQ= MIME-Version: 1.0 In-Reply-To: <20171221114144.2610d49b@bbrezillon> References: <20171214151610.19153-1-boris.brezillon@free-electrons.com> <20171214151610.19153-6-boris.brezillon@free-electrons.com> <20171216172040.jcaezouqkeb7zrqy@rob-hp-laptop> <20171216193537.0aef2e97@bbrezillon> <20171220180645.pis34opfwawakmqc@rob-hp-laptop> <20171221114144.2610d49b@bbrezillon> From: Rob Herring Date: Tue, 26 Dec 2017 12:29:34 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 5/7] dt-bindings: i3c: Document core bindings To: Boris Brezillon Cc: Wolfram Sang , linux-i2c@vger.kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org, Greg Kroah-Hartman , Arnd Bergmann , Przemyslaw Sroka , Arkadiusz Golec , Alan Douglas , Bartosz Folta , Damian Kos , Alicja Jurasik-Urbaniak , Cyprian Wronka , Suresh Punnoose , Thomas Petazzoni , Nishanth Menon , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , "linux-kernel@vger.kernel.org" , Vitor Soares , Geert Uytterhoeven , Linus Walleij Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5823 Lines: 126 On Thu, Dec 21, 2017 at 4:41 AM, Boris Brezillon wrote: > On Wed, 20 Dec 2017 12:06:45 -0600 > Rob Herring wrote: > >> On Sat, Dec 16, 2017 at 07:35:37PM +0100, Boris Brezillon wrote: >> > On Sat, 16 Dec 2017 11:20:40 -0600 >> > Rob Herring wrote: >> > >> > > On Thu, Dec 14, 2017 at 04:16:08PM +0100, Boris Brezillon wrote: >> > > > A new I3C subsystem has been added and a generic description has been >> > > > created to represent the I3C bus and the devices connected on it. >> > > > >> > > > Document this generic representation. >> >> [...] >> >> > > So please define the node >> > > name to be "i3c-controller". That's more inline with other node names >> > > than i3c-master that you used below. >> > >> > Hm, not sure i3c-controller is appropriate though, because you can have >> > slave controllers. Maybe i3c-host, but I'd prefer to keep the term >> > master since it's employed everywhere in the spec. I can also be >> > i3c-master-controller if you prefer. >> >> Okay, i3c-master is fine. Just make it explicit. > > Okay. > >> >> > > > +I3C devices >> > > > +=========== >> > > > + >> > > > +All I3C devices are supposed to support DAA (Dynamic Address Assignment), and >> > > > +are thus discoverable. So, by default, I3C devices do not have to be described >> > > > +in the device tree. >> > > > +This being said, one might want to attach extra resources to these devices, >> > > > +and those resources may have to be described in the device tree, which in turn >> > > > +means we have to describe I3C devices. >> > > > + >> > > > +Another use case for describing an I3C device in the device tree is when this >> > > > +I3C device has a static address and we want to assign it a specific dynamic >> > > > +address before the DAA takes place (so that other devices on the bus can't >> > > > +take this dynamic address). >> > > > + >> > > > +Required properties >> > > > +------------------- >> > > > +- i3c-pid: PID (Provisional ID). 64-bit property which is used to match a >> > > > + device discovered during DAA with its device tree definition. The >> > > > + PID is supposed to be unique on a given bus, which guarantees a 1:1 >> > > > + match. This property becomes optional if a reg property is defined, >> > > > + meaning that the device has a static address. >> > > >> > > What determines this number? >> > >> > Part of it is fixed (manufacturer and part id) and the last few bits >> > represent the device instance on the bus (so you can have several >> > identical devices on the same bus). The manufacturer and part ids >> > should be statically assigned during production, instance id is usually >> > configurable through extra pins that you drive high or low at reset >> > time. >> >> Sounds like an I2C address at least for the pin strapping part... > > The address space of this instance-id is smaller (4bits) than the I2C > one (7bits), and more importantly, the instance-id is not required to > be unique, it's the aggregation of the vendor-id, part-id and > instance-id that has to be unique. So, if you were thinking about using > this id to uniquely identify the device on the bus it's not a good idea. No, no. I was just commenting how I2C devices typically do the same pin strapping to make addresses unique. >> > > > +Optional properties >> > > > +------------------- >> > > > +- reg: static address. Only valid is the device has a static address. >> > > > +- i3c-dynamic-address: dynamic address to be assigned to this device. This >> > > > + property depends on the reg property. >> > > >> > > Perhaps "assigned-address" property would be appropriate. I'm not all >> > > that familiar with it though. >> > >> > Again, the spec use the term "dynamic address" everywhere, and I'd like >> > to stay as close as possible to the spec. >> >> I looked at assigned-addresses a bit more and that won't really fit >> because it should be the same format as reg. So I think reg should >> always be the PID as that is fixed and always present. Then the DAA >> address is separate and can be the i3c-dynamic-address property. >> >> However, there's still part I don't understand... >> >> > > > + /* I3C device with a static address. */ >> > > > + thermal_sensor: sensor@68 { >> > > > + reg = <0x68>; >> > > > + i3c-dynamic-address = <0xa>; >> >> I'm confused as to how/why you have both reg and dynamic address? > > Some I3C devices have an I2C address (also called static or legacy > address in a few places). The static/I2C/legacy address is used until > the I3C device is assigned a dynamic address by the master. The whole > point of specifying both an I2C address (through the reg property) and > a dynamic address (through the i3c-dynamic-address) is to tell the > controller that a specific dynamic address should be assigned to this > device using the SETSADA (Set Dynamic Address from Static Address) > command before a DAA (Dynamic Address Assignment) procedure is started. > This way, the device will not participate to the DAA (because it > already has a valid DA) and the dynamic address can't be assigned to > a different device (which is one of the problem with the automatic DAA > procedure). Okay, think I got it now. I think we should extend "reg" to have either I2C address, I3C PID, or both (in a defined order). I'm assuming you can always distinguish a static I2C address and an I3C PID just by upper bits all being 0s for I2C addresses. Maybe both is not needed? This means we'd have to allow 64-bit I2C addresses (#address-cells=2), but that should be easily fixed if that causes problems in the kernel. So i3c-pid would go away and i3c-dynamic-address stays. Rob